<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>代码雨</title>
</head>
<body> <canvas id="canvas"></canvas>
    <style type="text/css">
        body {
            margin: 0;
            padding: 0;
            overflow: hidden;
        }
    </style>
    <script type="text/javascript">
        var canvas = document.getElementById('canvas');
        var ctx = canvas.getContext('2d');
 
 
        canvas.height = window.innerHeight;
        canvas.width = window.innerWidth;
 
        var texts = '156dsfcac'.split('');
 
        var fontSize = 16;
        var columns = canvas.width / fontSize;
        // 用于计算输出文字时坐标，所以长度即为列数
        var drops = [];
        //初始值
        for (var x = 0; x < columns; x++) {
            drops[x] = 1;
        }
 
        function draw() {
            //让背景逐渐由透明到不透明
            ctx.fillStyle = 'rgba(0, 0, 0, 0.05)';
            ctx.fillRect(0, 0, canvas.width, canvas.height);
            //文字颜色
            ctx.fillStyle = '#0F0';
            ctx.font = fontSize + 'px arial';
            //逐行输出文字
            for (var i = 0; i < drops.length; i++) {
                var text = texts[Math.floor(Math.random() * texts.length)];
                ctx.fillText(text, i * fontSize, drops[i] * fontSize);
 
                if (drops[i] * fontSize > canvas.height || Math.random() > 0.95) {
                    drops[i] = 0;
                }
 
                drops[i]++;
            }
        }
        setInterval(draw, 33);
    </script>
</body>
</html>